A good tip, and this applies to other games as well, is if you have been using the Computer for a few hours beforehand, and then decide to Load, and run, the Flight Sim, is to switch off the Computer first, wait a few minutes, switch back on, and then Load the game.
This will have allowed the RAM to be cleared and refreshed, ready for the new Game installation...

...!
...also...make sure you have no unnecessary other programs running in the background..

...!
I have an Nvidia GF 7800 GS 256MB (AGP) Card, AMD Socket A Athlon 2600+ (2.1.GB) Processor, and 2.3 GB of RAM...
...and FS 2004 runs smoothly, with everything maxed, and no stuttering input from the Hard Drive!...

...!
F....with an ancient, but satisfactory system... [smiley=thumbsup.gif]...!
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.